What are the common processing techniques for injection molding of plastic products for home appliances?

In recent years, some new plastic processing technologies and new equipment have been widely used in the molding of household electrical appliances, such as precision injection molding, rapid prototyping technology, melt injection molding technology, gas-assisted/water-assisted injection molding technology, electromagnetic dynamic injection molding technology and Film injection molding technology.

Precision injection molding guarantees high precision and repeatability in terms of size and weight. Injection molding machines using this technology can achieve high pressure, high speed injection. Since the control method is usually open-loop or closed-loop control, high-precision control of the injection molding process parameters is possible. In general, precision injection molding requires high precision for the mold. At present, small and medium-sized precision injection molding machines have been produced in China.

Rapid prototyping technology is rapidly developed along with the development of home appliances in various diversification directions and continuous upgrading. It is mainly used to prepare plastic casings for home appliances. The advantage of this technology is that small batch production of plastic parts can be achieved without the need for a mold. At present, more mature rapid prototyping methods include laser scanning molding and liquid photocuring molding, among which laser scanning molding is widely used. The laser scanning device is composed of a laser light source, a scanning device, a dusting device and a computer. The processing process is that the laser head controlled by the computer scans according to a certain trajectory. At the position where the laser passes, the plastic micropowder is melted and bonded together by heat, and each time the scanning is finished, the micro powder device is sprinkled with a thin powder, so that After repeated scanning, an article having a certain shape and size is formed. At present, some enterprises in China have been able to produce laser scanning molding machines and plastic micro-powders, but the performance of the equipment is unstable, and the number of micro-powders is also small.

Fuse injection molding techniques are commonly used to shape shaped hollow articles that require high cavity roughness and precision and cannot be processed by hollow forming or rotational forming processes. At present, the application of this technology in foreign countries is relatively mature, but it is still in an individual application state in China. The processing principle of this technology is that the core shape constituting the cavity is first formed, and then the core type is used as an insert for injection molding. Under the heating of the injection molded part, the core type is melted and flowed out, thereby forming a cavity. The most important point in using this technology is the need to master the melting point of core materials and plastic parts. Generally, the core material may be a general-purpose plastic, a thermoplastic elastomer or a low-melting metal such as lead, tin or the like depending on the case.

Gas-assisted/water-assisted injection molding is widely used to form a variety of injection molded parts, and its typical product is a TV casing. When injection molding, gas or superheated water can be injected into the cavity almost simultaneously with the plastic melt. At this time, the plastic melt is coated with gas or superheated water, and the formed plastic product is a sandwich structure. After the plastic part is shaped, the gas or water can be discharged to release the mold. Such products have the advantages of material saving, small shrinkage, good appearance and good rigidity. A key part of the molding equipment is the gas-assisted or water-assisted device and its control software. In recent years, although there are many researches in China and the application speed is fast, domestic equipment is still unstable. Electromagnetic dynamic injection molding technology was invented by Mr. Jin Jinping from South China University of Technology. This technique causes the screw to reciprocate in the axial direction by the action of electromagnetic force. Since the plastic is microplasticized in the pre-plasticizing stage, the plastic structure of the pressure-holding stage is made denser and the internal stress of the product is reduced. This technology can be used to form more demanding articles such as optical discs. When used in the molding of common products, the quality of the product can be improved.

The application of film injection molding technology and equipment in foreign countries has been relatively mature. When using this technology, it is necessary to sandwich a special printed decorative plastic film into the mold before injection molding, and then injection molding. After being deformed by heat, the printed film can be attached to the surface of the plastic part, which is not only beautiful and firm, but also eliminates the post-decoration step.

Under normal circumstances, the demand for plastic molds for household appliances and plastic products is very large. For example, a plastic mold for a refrigerator or a fully automatic washing machine usually exceeds 100 pairs, and an air conditioner requires more than 20 pairs of one color TV. The machine requires 50-70 plastic molds. At the same time, the technical requirements for plastic molds are relatively high, and often the mold processing cycle is required to be as short as possible, thereby greatly promoting the development of mold design and modern mold manufacturing technology. In addition, some of the more difficult molds, such as hot runner injection molds, laminated injection molds, etc., are gradually increasing in China.